1. Technical Field
The present disclosure relates to the operation of a demodulator as part of a number of sub-circuits that operate together to process a data stream, and more particularly the present disclosure relates to the use of a demodulation bitmap of mask values to control the operation of a demodulator.
2. Background Information
Wireless communication systems are widely used to communicate various types of data including voice and video. Commonly, these systems are multiple-access systems capable of supporting communication with multiple users by sharing available system resources such as bandwidth and transmission power. Examples of multiple access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Long Term Evolution (LTE), and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
The transmission of a data stream using any of the aforementioned communication systems typically involves coding, multiplexing, and modulating the data stream. In addition, pilot data are typically multiplexed with the coded data. Pilot data of known patterns are processed in a known manner and may be used by the receiver system to estimate channel response. Modulation is typically performed based on a particular modulation scheme such as BPSK, QPSK, 16 QAM, or 64 QAM to map the data stream into a sequence of modulation symbols, for example Orthogonal Frequency Division Multiplex (OFDM) symbols, which may be further processed before transmission.
Receiving a data stream typically involves demodulating a received {I,Q} data symbol stream, followed by a process of demapping and decoding to recover the original data stream. The demapping process typically includes a Log-Likelihood Ratio (LLR) generator responsible for generating LLR values useable by the decoder. In a typical system, an LLR value is generated for each {I,Q,SNR} demodulated symbol value or “triplet.” However, some symbols are pilot symbols, useful for channel detection, but not for the recovery of the original data stream. LLR values generated from these pilot symbols may be significant in magnitude relative to non-pilot data symbols and may degrade decoder performance. Furthermore, the process of demodulating, generating LLR values, and decoding pilot symbols wastes power and processing throughput. In addition, some data symbols are known to be corrupted before the demodulation step. Similarly, it is desirable to avoid wasting power processing corrupted data symbols and propagating errors further down the signal processing chain.